hatchet man vs helper

hatchet man and helper both are nouns.

Word	Noun	Adjective	Verb	Adverb
hatchet man	Yes	No	No	No
helper	Yes	No	No	No

As nouns, helper is a hypernym of hatchet man; that is, helper is a word with a broader meaning than hatchet man:

hatchet man: one whose job it is to execute unpleasant tasks for a superior
helper: a person who contributes to the fulfillment of a need or furtherance of an effort or purpose

Other hypernyms of hatchet man include assistant, help, supporter.

hatchet man (noun)	helper (noun)
one whose job it is to execute unpleasant tasks for a superior	a person who helps people or institutions (especially with financial help)
a professional killer	a person who contributes to the fulfillment of a need or furtherance of an effort or purpose